I think of it this way: Consider radio telescopes. Ask "what was the first one of these?" The trail points back to Jansky's rotating directional antenna. I am happy to grant it the title of "first radio telescope," but I am a relaxed kind of guy.

Those who want to get into semantics and hair-splitting will want to consult Cosmic Noise: A History of Early Radio Astronomy by Woodruff T. Sullivan III, which is a rich source of information on Jansky, Reber, their contemporaries, and observers who preceded them.